Mac OS X 10.4 Tiger

"For Tiger, Apple created launchd: one launch daemon to rule them all. Launchd does the job of all of the existing program launching mechanisms, and does it in a way that puts the least possible burden on the programs that it launches. Processes spawned by launchd don't have to worry about "daemonizing" themselves, checking for dependencies, or relaunching or keeping communication handles alive in the case of a crash."Story